Question: What decays to Uranium-238, which has a proton number of 90?
Paraphrase: What rots to Uranium-238, which features a proton number of 90?
SPARQL (Wikidata): SELECT ?answer WHERE { wd:Q1148503 wdt:P816 ?answer . ?answer wdt:P1086 ?x FILTER(contains(?x , '90'))}
Answer: thorium-234